- Make the HTTP, FTP and file channels implement nsIPropertyBag2 and associated
interfaces (by inheriting from nsHashPropertyBag)
- Use that interface to expose a "content-length" property giving the length of
the data as a 64-bit value on the FTP and HTTP channels
- change docshell and xpinstall to use nsIPropertyBag2 instead of nsIProperties
to read/write the referrer property